Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and an apparatus including processing circuitry that decodes coded information of a coding block (CB) in a picture from a coded video bitstream. The coded information indicates a width W and a height H of the CB. The processing circuitry partitions the CB into sub-processing units (SPUs) having a width being a minimum one of W and K and a height being a minimum one of H and K. At least one of the width W and the height H is larger than a processing data unit size K. The processing circuitry determines a partitioning structure to partition the SPUs based on the width, the height, and a maximum transform unit (TU) size M. At least one of the width and the height is larger than M. The processing circuitry partitions each of the SPUs into TUs of M×M based on the partitioning structure.

INCORPORATION BY REFERENCE

This present application claims the benefit of priority to U.S.Provisional Application No. 62/822,787, “Modified VPDU Compatible MaxTransform Control” filed on Mar. 22, 2019, which is incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1 , depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEMNVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 2 , a current block (201) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (202 through 206, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes processing circuitry. The processing circuitry is configured todecode coded information of a coding block (CB) in a picture from acoded video bitstream. The coded information indicates a width of Wsamples and a height of H samples of the CB. The processing circuitrycan partition the CB into sub-processing units (SPUs) having a widththat is a minimum one of W and K and a height that is a minimum one of Hand K. At least one of the width W and the height H of the CB is largerthan a processing data unit size K. The processing circuitry candetermine a partitioning structure to further partition the SPUs basedon the width and the height of the SPUs and a maximum transform unit(TU) size of M samples. At least one of the width and the height of theSPUs is larger than M. The processing circuitry can partition each ofthe SPUs into TUs of M×M based on the determined partitioning structure.

In an embodiment, the width and the height of the SPUs are larger thanM. The processing circuitry can determine the partitioning structure tobe a quadtree partitioning structure. The processing circuitry canpartition the SPUs into the TUs based on the quadtree partitioningstructure.

In an embodiment, the width of the SPUs is larger than M and the heightof the SPUs is equal to M. The processing circuitry can determine thepartitioning structure to be a vertical binary tree partitioningstructure. The processing circuitry can partition the SPUs into the TUsbased on the vertical binary tree partitioning structure.

In an embodiment, the height of the SPUs is larger than M and the widthof the SPUs is equal to M. The processing circuitry can determine thepartitioning structure to be a horizontal binary tree partitioningstructure. The processing circuitry can partition the SPUs into the TUsbased on the horizontal binary tree partitioning structure.

In an embodiment, the processing circuitry can partition one of the SPUsrecursively into the TUs based on the partitioning structure.

In an embodiment, the processing circuitry can process the SPUsaccording to a first scan order, and process the TUs in each of the SPUsaccording to a second scan order. In an example, at least one of thefirst scan order and the second scan order is one of (i) a raster scanorder, (ii) a vertical scan order, (iii) a zig-zag order, and (iv) adiagonal scan order. In an example, the first scan order and the secondscan order are the raster scan order. In an example, W is 128, H is 64,K is 64, and M is 32. The first scan order is from left to right and thesecond scan order is a raster scan order.

In an embodiment, the processing data unit size K indicates a size of avirtual pipeline data unit (VPDU). A first one of the SPUs is includedin a first VPDU and a second one of the SPUs is included in a secondVPDU in the picture. After processing the first VPDU in a first stage ofa multi-stage pipeline, the processing circuitry can simultaneouslyprocess the first VPDU in a second stage of the multi-stage pipeline andthe second VPDU in the first stage.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9A shows a CTU that is partitioned with a quadtree plus binary tree(QTBT) structure (910).

FIG. 9B shows the QTBT structure (920).

FIG. 9C shows a horizontal center-side triple-tree.

FIG. 9D shows a vertical center-side triple-tree.

FIGS. 10A-10D show transform core matrices of 4-point, 8-point, 16-pointand 32-point DCT-2 transform, respectively.

FIGS. 11A-11E show a 64×64 transform core matrix of the 64-point DCT-2transform.

FIG. 12 shows transform basis functions of the selected discrete sinetransform (DST)/discrete cosine transform (DCT) transforms of anadaptive multiple transform (AMT).

FIG. 13 shows a table (1300) illustrating a mapping relationship betweenan mts_idx value and respective horizontal or vertical transforms.

FIGS. 14A-14D show transform core matrices of DST-7 transform.

FIGS. 15A-15D show transform core matrices of DCT-8 transform.

FIG. 16 shows a number of sub-partitions depending on a block size.

FIG. 17 shows an example of an intra sub-partition (ISP).

FIG. 18 shows an example of an ISP.

FIGS. 19A-19B show an example of syntax elements (1900) for an ISPcoding mode.

FIGS. 20A-20D show examples of a sub-block transform (SBT).

FIGS. 21A-21I show an example of a specification text of a video codingstandard when SBT is used.

FIG. 22 shows different YUV formats used in some embodiments.

FIG. 23 shows examples of disallowed ternary tree (TT) and binary tree(BT) partitioning.

FIG. 24 shows an example of transform tree syntax.

FIG. 25 shows a coding block (2510) having a size of 128×64 samples.

FIG. 26A shows a coding block (2610A) having a size of 128×32 samples.

FIG. 26B shows a coding block (2610B) having a size of 128×32 samples.

FIG. 27 shows a flow chart outlining a process (2700) according to anembodiment of the disclosure.

FIG. 28 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS I. Video Coding Encoder and Decoder

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

II. Transform Processing Techniques 1. Block Partitioning StructureIncluding a Quadtree Partitioning Structure

A block partitioning structure can be referred to as a coding tree. Insome embodiments, by using a quadtree structure, a coding tree unit(CTU) is split into coding units (CUs) to adapt to various localcharacteristics. A decision on whether to code a picture area using aninter-picture (temporal) or intra-picture (spatial) prediction is madeat CU level. Each CU can be further split into one, two, or fourprediction units (PUs) according to a PU splitting type. Inside one PU,a same prediction process is applied and relevant information istransmitted to a decoder on a PU basis.

After obtaining a residual block by applying a prediction process basedon the PU splitting type, a CU can be partitioned into transform units(TUs) according to another quadtree structure. As can be seen, there aremultiple partition conceptions including CU, PU, and TU. In someembodiments, a CU or a TU can only be square shape, while a PU may besquare or rectangular shape. In some embodiments, one coding block maybe further split into four square sub-blocks, and transform is performedon each sub-block, i.e., TU. Each TU can be further split recursivelyinto smaller Tus using a quadtree structure which is called residualquadtree (RQT).

At a picture boundary, in some embodiments, implicit quadtree split canbe employed so that a block will keep quad-tree splitting until the sizefits the picture boundary.

2. Quadtree Plus Binary Tree (QTBT) Block Partitioning Structure

In some embodiments, a quadtree plus binary tree (QTBT) structure isemployed. The QTBT structure removes the concepts of multiple partitiontypes (the CU, PU and TU concepts), and supports more flexibility for CUpartition shapes. In the QTBT block structure, a CU can have either asquare or rectangular shape.

FIG. 9A shows a CTU (910) that is partitioned by using a QTBT structure(920) shown in FIG. 9B. The CTU (910) is first partitioned by a quadtreestructure. The quadtree leaf nodes are further partitioned by a binarytree structure or a quadtree structure. There can be two splittingtypes, symmetric horizontal splitting and symmetric vertical splitting,in the binary tree splitting. The binary tree leaf nodes are called CUsthat can be used for prediction and transform processing without anyfurther partitioning. Accordingly, CU, PU and TU have the same blocksize in the QTBT coding block structure.

In some embodiments, a CU can include coding blocks (CBs) of differentcolor components. For example, one CU contains one luma CB and twochroma CBs in the case of P and B slices of the 4:2:0 chroma format. ACU can include a CB of a single color component. For example, one CUcontains only one luma CB or just two chroma CBs in the case of Islices.

The following parameters are defined for the QTBT partitioning scheme insome embodiments:

-   -   CTU size: the root node size of a quadtree, e.g. the same        concept as in HEVC.    -   MinQTSize: the minimum allowed quadtree leaf node size.    -   MaxBTSize: the maximum allowed binary tree root node size.    -   MaxBTDepth: the maximum allowed binary tree depth.    -   MinBTSize: the minimum allowed binary tree leaf node size.

In one example of the QTBT partitioning structure, the CTU size is setas 128×128 luma samples with two corresponding 64×64 blocks of chromasamples, the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64,the MinBTSize (for both width and height) is set as 4×4, and theMaxBTDepth is set as 4. The quadtree partitioning is applied to the CTUfirst to generate quadtree leaf nodes. The quadtree leaf nodes may havea size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size).If the leaf quadtree node is 128×128, it will not be further split bythe binary tree since the size exceeds the MaxBTSize (i.e., 64×64).Otherwise, the leaf quadtree node could be further partitioned by thebinary tree. Therefore, the quadtree leaf node is also the root node forthe binary tree and it has the binary tree depth as 0.

When the binary tree depth reaches MaxBTDepth (i.e., 4), no furthersplitting is considered. When the binary tree node has width equal toMinBTSize (i.e., 4), no further horizontal splitting is considered.Similarly, when the binary tree node has height equal to MinBTSize, nofurther vertical splitting is considered. The leaf nodes of the binarytree are further processed by prediction and transform processingwithout any further partitioning. In an embodiment, a maximum CTU sizeis 256×256 luma samples.

In FIGS. 9A and 9B, the solid lines indicate quadtree splitting anddotted lines indicate binary tree splitting. In each splitting (i.e.,non-leaf) node of the binary tree, one flag is signaled to indicatewhich splitting type (i.e., horizontal or vertical) is used. Forexample, 0 indicates a horizontal splitting and 1 indicates a verticalsplitting. For the quadtree splitting, there is no need to indicate thesplitting type since quadtree splitting always splits a block bothhorizontally and vertically to produce 4 sub-blocks with an equal size.

In some embodiments, the QTBT scheme supports the flexibility for theluma and chroma to have a separate QTBT structure. For example, for Pand B slices, the luma and chroma blocks in one CTU share the same QTBTstructure. However, for I slices, the luma CTB is partitioned into CUsby a QTBT structure, and the chroma blocks are partitioned into chromaCUs by another QTBT structure. Thus, a CU in an I slice consists of acoding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice consists of coding blocks of allthree color components.

In some embodiments, inter prediction for small blocks is restricted toreduce memory access of motion compensation. For example, bi-predictionis not supported for 4×8 and 8×4 blocks, and inter prediction is notsupported for 4×4 blocks.

3. Ternary Tree (TT) Block Partitioning Structure

In some embodiments, a multi-type-tree (MTT) structure is used forpartitioning a picture. The MTT structure is a more flexible treestructure than the QTBT structure. In MTT, in addition to quad-tree andbinary-tree, horizontal center-side triple-tree and vertical center-sidetriple-tree as shown in FIG. 9C and FIG. 9D, respectively, are employed.Triple tree partitioning can complement quad-tree and binary-treepartitioning. For example, triple-tree partitioning is able to captureobjects which locate in a block center, while quad-tree and binary-treecan split crossing block centers. The width and height of partitions bytriple trees are a power of 2 so that no additional transform partitionis needed.

In an example, the design of a two-level tree is mainly motivated bycomplexity reduction. For example, the complexity of traversing of atree is T^(D), where T denotes a number of split types, and D is a depthof tree.

4. Primary Transform Examples

In some embodiments, such as in HEVC, 4-point, 8-point, 16-point and32-point DCT-2 transforms are used as primary transforms. FIGS. 10A-10Dshow transform core matrices of 4-point, 8-point, 16-point, and 32-pointDCT-2, respectively. Elements of those transform core matrices can berepresented using 8-bit integers, and thus those transform core matricesare referred to as 8-bit transform cores. As shown, the transform corematrix of a smaller DCT-2 is a part of that of a larger DCT-2.

The DCT-2 core matrices show symmetry/anti-symmetry characteristics.Accordingly, a so-called “partial butterfly” implementation can besupported to reduce the number of operation counts (multiplications,adds/subs, shifts). Identical results of matrix multiplication can beobtained using the partial butterfly implementation.

5. Additional Primary Transform Examples

In some embodiments, in addition to 4-point, 8-point, 16-point and32-point DCT-2 transforms described above, additional 2-point and64-point DCT-2 are used. FIGS. 11A-11E shows a 64×64 transform corematrix of the 64-point DCT-2 transform.

In some embodiments, in addition to DCT-2 and 4×4 DST-7 transforms, anadaptive multiple transform (AMT) (also known as enhanced multipletransform (EMT), or multiple transform selection (MTS)) is used forresidual coding of both inter and intra coded blocks. The AMT usesmultiple selected transforms from discrete cosine transform(DCT)/discrete sine transform (DST) families in addition to DCT-2transforms, such as transform core matrices of DST-7, or DCT-8transform. FIG. 12 shows transform basis functions of the selectedDST/DCT transforms.

In some embodiments, the DST/DCT transform core matrices used in AMT arerepresented with 8-bit representation. In some embodiments, AMT isapplied to CUs with both width and height smaller than or equal to 32.Whether to apply AMT or not can be controlled by a flag (e.g., an mtsflag). For example, when the mts flag is equal to 0, only DCT-2 isapplied to coding a residue block. When the mts flag is equal to 1, anindex (e.g., an mts_idx), can further be signaled using 2 bins tospecify a horizontal and vertical transforms to be used.

FIG. 13 shows a table (1300) illustrating a mapping relationship betweenthe index (e.g., the mts_idx) value and respective horizontal orvertical transforms. A row (1301) with the mts_idx having a value of −1corresponds to the scenario where the flag (e.g., the mts flag) is equalto 0, and DCT-2 transform is used. Rows (1302)-(1305) with the mts_idxhaving a value of 0, 1, 2, or 3 correspond to the scenario where the mtsflag is equal to 1. In the right two columns of the table (1300), 0represents a transform type of DCT-2, 1 represents a transform type ofDST-7, and 2 represents a transform type of DCT 8.

FIGS. 14A-14D show transform core matrices of DST-7 transform. FIGS.15A-15D show transform core matrices of DCT-8 transform.

6. Intra Sub-Partition (ISP) Coding Mode

In some embodiments, an intra sub-partition (ISP) coding mode isemployed. In ISP coding mode, a luma intra-predicted block can bepartitioned vertically or horizontally into 2 or 4 sub-partitions. Thenumber of sub-partitions can depend on a size of the block. FIG. 16shows the number of sub-partitions depending on the block size. FIG. 17shows an example where a block of 4×8 or 8×4 is partitioned into twosub-partitions. FIG. 18 shows an example where a block having a sizethat is larger than 4×8 or 8×4 is partitioned into four sub-partitions.In an example, all sub-partitions fulfill a condition of having at least16 samples. In an example, ISP is not applied to chroma components.

In an example, for each of sub-partitions partitioned from a codingblock, a residual signal is generated by entropy decoding respectivecoefficients sent from an encoder and then inverse quantizing andinverse transforming them. Then, a first one of the sub-partitions isintra predicted to generate a prediction signal. The prediction signalis added to the respective residual signal of the first sub-partition toobtain corresponding reconstructed samples. Thereafter, thereconstructed sample values of the first sub-partition can be availableto generate a prediction of a second one of the sub-partitions. Thisprocess can be repeated sub-partition by sub-partition, until allsub-partitions from the coding block are reconstructed. In an example,all the sub-partitions share a same intra mode.

In an embodiment, the ISP coding mode is only tested with intra modesthat are part of a most probable mode (MPM) list. Accordingly, if ablock uses ISP, then a MPM flag can be inferred to be one. In addition,when ISP is used for a certain block, then a respective MPM list will bemodified to exclude DC mode and to prioritize horizontal intra modes forthe ISP horizontal split and vertical intra modes for the vertical one.

In ISP coding mode, each sub-partition can be regarded as a TU, sincethe transform and reconstruction is performed individually for eachsub-partition.

FIGS. 19A-19B shows an example of syntax elements (1900) signaled for anISP coding mode. As shown in a frame (1910), a syntax element, e.g.,intra subpartitions mode flag, indicates whether ISP is used or not. Asyntax element, e.g., intra subpartitions split flag, indicates apartition direction (vertical or horizontal).

7. Sub-Block Transform (SBT)

In some embodiments, a sub-block transform (SBT), also referred to asspatially varying transform (SVT), is employed. The SBT can be appliedto inter prediction residuals. In some examples, residual block isincluded in the coding block and is smaller than the coding block. Thusa transform size in SBT is smaller than the coding block size. For theregion which is not covered by the residual block, zero residual can beassumed, and thus no transform processing is performed.

FIGS. 20A-20D shows sub-block types (SVT-H, SVT-V) (e.g., horizontallyor vertically partitioned), sizes and positions (e.g., left half, leftquarter, right half, right quarter, top half, top quarter, bottom half,bottom quarter) supported in SBT. The shaded regions labeled by letter“A” is residual blocks with transform, and the other regions is assumedto be zero residual without transform.

As an example, FIGS. 21A-21I show changes to a specification text of avideo coding standard (e.g., VVC) when SBT is used. The added texts areshown in frames from (2101) to (2113). As shown, additional syntaxelements, e.g., additional overhead bits cu_sbt_flag, cu_sbt_quad_flag,cu_sbt_horizontal_flag, and cu_sbtpos_flag, can be signaled to indicatethe sub-block type (horizontal or vertical), size (half or quarter) andposition (left, right, top or bottom), respectively.

8. YUV Formats

FIG. 22 shows different YUV formats (e.g., 4:4:4, 4:2:2, 4:1:1, and4:2:0) used in some embodiments. In an example, a cross component linearmodel intra prediction is used for the 4:2:0 format. A six-tapinterpolation filter can be applied to obtain a down-sampled luma samplecorresponding to a chroma sample as shown in FIG. 22 . In an example, adown-sampled luma sample Rec′L[x, y] can be calculated from nearbyreconstructed luma samples (represented by Rec_(L)[x, y]) as follows:Rec′_(L)[x,y]=(2×Rec_(L)[2x,2y]+2×Rec_(L)[2x,2y+1]+Rec_(L)[2x−1,2y]+Rec_(L)[2x+1,2y]+Rec_(L)[2x−1,2y+1]+Rec_(L)[2x+1,2y+1]+4)>>3

The down-sampled luma sample Rec′L[x, y] can be used to predict a chromasample using a cross component linear model mode.

9. Virtual Pipeline Data Unit (VPDU)

Virtual pipeline data units (VPDUs) can be defined as non-overlappingM×M-luma (L)/N×N-chroma (C) units in a picture. In some hardware decoderimplementations, successive VPDUs are processed by multiple pipelinestages at the same time. Different stages process different VPDUssimultaneously. A VPDU size can be roughly proportional to a buffer sizein pipeline stages, so that it is desired to keep the VPDU size at acertain size (e.g., 64×64 or smaller). In certain decoders, a VPDU sizeis set to a maximum transform unit (TU) size. Enlarging a maximum TUsize from 32×32-L/16×16-C in HEVC to 64×64-L/32×32-C in current VVC canbring a coding gain, which expectedly results in 4 times of VPDU size incomparison with HEVC. However, BT and TT structures that are adopted inVVC for achieving additional coding gains can be applied to128×128-L/64×64-C coding tree blocks recursively, leading to 16 times ofVPDU size (128×128-L/64×64-C) in comparison with HEVC.

FIG. 23 shows certain TT and BT partitioning that are disallowed.

In order to keep the VPDU size as 64×64 luma samples, certain partitionrestrictions (with syntax signaling modification) are applied in someembodiments:

-   -   TT split is not allowed for a CU with either width or height, or        both width and height equal to 128.    -   For a 128×N CU with N≤64 (i.e., width equal to 128 and height        smaller than 128), horizontal BT is not allowed.    -   For an N×128 CU with N≤64 (i.e., height equal to 128 and width        smaller than 128), vertical BT is not allowed.

III. Transform Block Partitioning and Processing Techniques

In some embodiments, a fixed maximum allowable transform unit (TU) sizeor maximum TU size (e.g., 64×64 pixels or samples) is used. In someembodiments, controllable or configurable maximum TU sizes are employedsince a maximum TU size can have an impact on hardware complexity, suchas for encoder implementation (e.g., pipeline intermediate buffer size,number of multipliers, and the like). For example, in addition to a sizeof 64×64 samples, a maximum TU size can be of other sizes, such as 32×32samples, 16×16 samples, or the like.

In certain video standards, SBT and ISP can be used. For example, inSBT, a SPS flag, e.g., sps_sbt_max_size 64 flag is signaled to indicatewhether a largest SBT size is 32-length or 64-length. Whensps_sbt_max_size 64 flag is true (i.e., the largest SBT size is64-length) and the maximum TU size is 32-point, an encoder crash may betriggered. In general, an L-length or L-point size refers to a maximumdimension of a CU, a TU, a CB, a TB, a VPDU, or the like. For example,when the maximum TU size is 32-point or 32-length, a width and a heightof a TU are less than or equal to 32.

In some embodiments, the ISP mode is allowed for various CU sizes,however, when the maximum TU size is set to be smaller than 64, aconflict can occur whether an implicit transform split is performed oran explicit transform split using ISP with signaling is performed. Forexample, when the maximum TU size is 16, for a 64×16 CU, without ISP,the CU can be implicitly split into four 16×16 TUs. With ISP, the 64×16CU may be partitioned with a vertical ISP and thus may be split intofour 16×16 TUs, but using signaling.

When the maximum TU size is smaller than 64×64, a TU processing order isneeded to align with an implementation of VPDUs.

Embodiments described herein may be used separately or combined in anyorder. Further, the embodiments may be implemented by processingcircuitry (e.g., one or more processors or one or more integratedcircuits) in an encoder, a decoder, or the like. In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium.

In the disclosure, a high-level syntax (HLS) element can refer to aVideo Parameter Set (VPS), a Sequence Parameter Set (SPS), a PictureParameter Set (PPS), a Slice header, a Tile header, a Tile group header,or the like. A CTU header can refer to syntax element(s) signaled for aCTU, e.g., as header information. In an example, a CTU size is a maximumCU size.

In general, when a luma size (represented by luma samples) of a certainunit (e.g., a TU, a CU) is known, a corresponding chroma size that isspecified by a number of chroma samples can be obtained. In an example,a YUV format is 4:2:0 is used and a CU has a CU size of 64×64 lumasamples (or 64×64-L). Accordingly, the CU has a CU size of 32×32 chromasamples (or 32×32-C). The CU size can be referred to as 64×64-L,32×32-C, or 64×64-L/32×32-C. Similarly, a TU has a TU size of 64×64 lumasamples (or 64×64-L). Accordingly, the TU has a TU size of 32×32 chromasamples (or 32×32-C). The TU size can be referred to as 64×64-L,32×32-C, or 64×64-L/32×32-C. For example, the TU includes a lumatransform block (TB) and two chroma TBs. The luma TB has a size of64×64-L and each of the chroma TBs has a size of 32×32-C. In general,embodiments and methods described for a CU or a TU can be suitablyadapted to a CB and a TB, respectively.

The CU can include a luma block of 64×64-L and two chroma blocks of32×32-C. In the descriptions below, a TU size is represented using lumasamples in the TU. For example, a maximum TU size of M samples refers toa maximum TU size of M luma samples. Similarly, other sizes, such as aVPDU size and a CU size, are also represented using respective lumasamples in corresponding units, such as a VPDU and a CU, respectively.Of course, the TU size, the VPDU size, the CU size, or the like can berepresented using chroma samples or a combination of luma and chromasamples.

A unit size may refer to a width, a height, or an area of the unit. Forexample, a maximum TU size may refer to a width, a height, or an area ofa maximum TU. In general, a TU, a CU, a VPDU, or the like can have anysuitable shape, including a rectangular shape, a square shape, an ‘L’shape, or any suitable shape. When the shape of the unit is irregular,such as an ‘L’ shape, the unit size can specify an area of the unit.

In some embodiments, a VPDU size and/or a maximum TU size can besignaled in a coded video bitstream, such as in a SPS and a PPS. Asdescribed above, the VPDU size and/or the maximum TU size can besignaled in terms of luma samples. Alternatively, the VPDU size and/orthe maximum TU size can be signaled in terms of chroma samples.

In some embodiments, a VPDU size and/or a maximum TU size can be storedin an encoder and/or a decoder, thus the VPDU size and/or the maximum TUsize is not signaled. In one example, the VPDU size and/or the maximumTU size can be stored in profile and/or level definitions. The VPDU sizeand/or the maximum TU size can be stored in terms of luma or chromasamples.

In some embodiments, VPDUs share the same size but may have differentshapes. For example, when a VPDU size is 4096 in terms of luma samples,the VPDU can have a square shape of 64×64 or a rectangular shape of32×128. The VPDU can also have other shapes, such as an L shape, as longas the VPDU size is 4096 in terms of luma samples. The above descriptionis also applicable to certain TUs.

1. Example A

According to aspects of the disclosure, a maximum allowable TU size(also referred to as a maximum TU size) is M samples (e.g., a size ofM×M samples). In an example, the maximum width and the maximum height ofthe TU is M. In an example, the maximum area of the TU is M×M. Aprocessing data unit size (such as a VPDU size) is K samples (e.g., asize of K×K samples). In an example, the maximum width and the maximumheight of the processing data unit size is K. In an example, the maximumarea of the processing data unit size is K×K. A CU of W×H has a width ofW samples and a height of H samples. The CU can be partitioned intomultiple sub-units, referred to as sub-processing units (SPUs), based onthe CU size and the processing data unit size K. The CU can bepartitioned into the SPUs using any suitable partitioning structures ora combination of any suitable partitioning structures, such as QTBT, QT,BT, TT, or a combination thereof. The SPUs may have a same size ordifferent sizes.

In an embodiment, the CU is partitioned into the SPUs when the width Wor the height H is larger than K. In an example, the SPUs have a samesize (i.e., a SPU size) and each SPU has a size of Min(W, K)×Min(H, K)samples. Thus, a width of each SPU is a minimum of W and K, and a heightof the SPU is a minimum of H and K. In some examples, prior topartitioning the CU, whether to partition the CU can be determined basedon the size of the CU and the processing data unit size K.

A SPU in the CU can be further partitioned into TUs having a size of,for example, M×M samples. In some examples, the SPU can be partitionedinto the TUs having a size of Min(W, K, M)×Min(H, K, M). In someexamples, prior to partitioning the SPU, whether to partition the SPUcan be determined based on the size of the SPU and the maximum TU sizeM. The SPU can be partitioned using any suitable partitioning structuresor a combination of any suitable partitioning structures, such as QTBT,QT, BT, TT, or a combination thereof. According to aspects of thedisclosure, one or more partitioning structures to partition the SPU canbe determined based on the size of the SPU and the maximum TU size M. Inan example, the SPU can be recursively split into the TUs using thedetermined one or more partitioning structures.

In an example, when the width and the height of the SPU are larger thanthe maximum TU size M, the SPU is split into the TUs of M×M using aquadtree partitioning structure. The SPU can be recursively split intothe TUs using the quadtree partitioning structure.

In an example, when the width of the SPU is larger than M and the heightof the SPU is equal to M, the SPU is split into the TUs of M×M using avertical binary tree partitioning structure. For example, M is 32 andthe SPU has a size of 64×32. Thus the width of the SPU is 64 and theheight of the SPU is 32. Accordingly, the vertical binary treepartitioning structure can be used to split the SPU into two TUs of32×32. The SPU can be recursively split into the TUs using the verticalbinary tree partitioning structure.

In an example, when the width of the SPU is larger than M and the heightof the SPU is less M, the SPU can be split into the TUs using thevertical binary tree partitioning structure where the width of the TUsis M and the height of the TUs is equal to the height of the SPU.

In an example, when the height of the SPU is larger than M and the widthof the SPU is equal to M, the SPU is split into the TUs of M×M using ahorizontal binary tree partitioning structure. The SPU can berecursively split into the TUs using the horizontal binary treepartitioning structure. For example, M is 32 and the SPU has a size of32×64. Thus the width of the SPU is 32 and the height of the SPU is 64.Accordingly, the horizontal binary tree partitioning structure can beused to split the SPU into two TUs of 32×32.

When the height of the SPU is larger than M and the width of the SPU isless M, the SPU can be split into the TUs using the horizontal binarytree partitioning structure where the height of the TUs is M and thewidth of the TUs is equal to the width of the SPU.

The transform tree syntax in FIG. 24 shows an example of splitting theSPU and a processing order used to process the TUs.

In an example, the CU of W×H can be partitioned in two steps. In a firststep, the CU is partitioned into the SPUs where each SPU has the size ofMin(W, K)×Min(H, K). Subsequently, in a second step, each SPU is furtherpartitioned into the TUs where each TU has the size of M×M.

When processing the TUs in the CU, the SPUs in the CU can be scanned andprocessed in a first scan order (also referred to as a first order).Further, within each of the SPUs, the TUs can be scanned and processedin a second order (also referred to as a second order).

In various embodiments, the first order for processing the SPUs can be araster scan order, a vertical scan order (e.g., scans SPUs column-wisefrom left to right or vice versa), a zig-zag order, a diagonal scanorder, or the like.

In various embodiments, the second order for processing the TUs withineach SPU can be a raster scan order, a vertical scan order (e.g., scansthe TUs column-wise from left to right or vice versa), a zig-zag order,a diagonal scan order, or the like.

The first order and the second order can be the same or different indifferent embodiments. For example, the first order for processing theSPUs and the second order for processing the TBs within each of the SPUsare both the raster scan order in an embodiment.

2. Example B

FIG. 25 shows a CU (2510) having a size of W×H samples where W=128, andH=64. A maximum TU size M is 32 samples. The processing data unit sizeK, such as a VPDU size, is 64 samples. The CU (2510) is first split intoa first 64×64 SPU (2520) and a second 64×64 SPU (2530). The first SPU(2520) and the second SPU (2530) can then be further partitioned intoTUs 0-7 each having a size of M×M samples. The TUs 0-3 are included inthe first SPU (2520), and the TUs 4-7 are included in the second SPU(2530).

According to the first order, the first SPU (2520) can first beprocessed followed by the second SPU (2530). Within the first SPU (2520)or the second SPU (2530), the second order used for processing the TUs0-3 or 4-7 is the raster scan order. Accordingly, the TUs 0-7 areprocessed according to an order indicated by arrows (2551). The firstorder and/or the second order can be determined explicitly (e.g., viasignaling from an encoder to a decoder) or implicitly.

In some examples, partitioning a CU into SPUs where each of the SPUsfurther includes TUs as described above improves coding efficiency.Referring to FIG. 25 , in an example, the first SPU (2520) is a firstVPDU and the second SPU (2530) is a second VPDU. Each of the first VPDU(or the first SPU (2520)) and the second VPDU (or the second SPU (2530))can sequentially pass through a multi-stage pipeline including a firststage (e.g., entropy decoding), a second stage (e.g., de-quantization),a third stage (e.g., an inverse transform), and/or the like. Accordingto the first order shown in FIG. 25 , the first SPU (2520) is to beprocessed prior to the second SPU (2530), thus the first SPU (2520) isprocessed by the first stage and then goes to the second stage. In anexample, when the first SPU (2520) is processed by the second stage, thesecond SPU (2530) is processed by the first stage to improve the codingefficiency. Subsequently, the first SPU (2520) goes to the third stageand the second SPU (2530) can move to the second stage. When the firstSPU (2520) is processed by the third stage, the second SPU (2530) can beprocessed by the second stage. The above description is given usingVPDUs and a multi-stage pipeline as an example and can be suitablyadapted to other architectures or video coding methods. The abovedescription can be adapted when the first SPU (2520) is included in thefirst VPDU and the second SPU (2530) is included in the second VPDU. Atleast a part of the processing of the SPUs in the different stages isperformed simultaneously.

As described above, when the SPU size is larger than the TU size,multiple TUs in the CU can be grouped into a processing data unit, suchas a SPU (or a VPDU) where the SPUs can be processed in a multi-stagepipeline that allows parallel processing (or simultaneous processing) ofsuccessive SPUs. In some examples, The description can be modified asfollows: the CU is partitioned into first units. Further, each of thefirst units can be partitioned into second units. Each of the secondunits may be partitioned into third units. In an example, a size of thefirst units is larger than a size of the second units, and the size ofthe second units is larger than a size of the third units. Suchpartitioning may be beneficial when a first multi-stage pipeline isnested within a second multi-stage pipeline.

3. Example C

FIG. 26A shows a CU (2610A) having a size of W×H samples where W=128,and H=32. The maximum TU size M is 16 samples. The processing data unitsize K, such as a VPDU size, is 64 samples. A minimum of W and K is 64,while a minimum of H and K is 32. Thus, a size of a SPU can bedetermined to be 64×32 samples, for example, to align transform blockswith VPDUs. The CU (2610A) can be partitioned into a left SPU (2620A)and a right SPU (2630A) each having a size of 64×32 samples. The twoSPUs (2620A) and (2630A) can be scanned and processed in an order fromleft to right.

Each of the two SPUs (2620A) and (2630A) can be further split into TUseach having the maximum TU size, 16×16 samples. As shown, the left SPU(2620A) is partitioned into the TUs 0-7, while the right SPU (2630A) ispartitioned into the TUs 8-15. In the SPU (2620A), the TUs 0-7 can beprocessed in the raster scan order. In the SPU (2630A), the TUs 8-15 canbe processed in the raster scan order. Accordingly, the TUs 0-15 can bescanned and processed in an order indicated by arrows (2651A) where theTU 0 is processed first and the TU 15 is processed after the TUs 0-14are processed.

4. Example D

FIG. 26B shows a CU (2610B) having a size of W×H samples where W=128,and H=32. The maximum TU size M is 16 samples. The processing data unitsize K, such as a VPDU size, is 64 samples. In a similar way as in theFIG. 25 example, the CU (2610B) can be partitioned into two SPUs (2620B)and (2630B) that can each be further partitioned into TUs. The SPUs(2620B) and (2630B) can be processed from left to right in the sameorder as in FIG. 25 . However, different from the FIG. 25 example, theTUs 0-7 in the SPU (2620B) are processed in the zig-zag scan order, andthe TUs 8-15 in the SPU (2630B) are processed in the zig-zag scan order.

5. Example E

FIG. 27 shows a flow chart outlining a transform block partitioning andprocessing process (2700) according to an embodiment of the disclosure.The process (2700) can be used in the reconstruction of a block coded inintra mode or inter mode. In various embodiments, the process (2700) areexecuted by processing circuitry, such as the processing circuitry inthe terminal devices (210), (220), (230) and (240), the processingcircuitry that performs functions of the video encoder (403), theprocessing circuitry that performs functions of the video decoder (310),the processing circuitry that performs functions of the video decoder(410), the processing circuitry that performs functions of the videoencoder (603), and the like. In some embodiments, the process (2700) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (2700). The process starts at (S2701) and proceeds to(S2710).

At (S2710), coded information of a CU in a picture can be decoded from acoded video bitstream. The coded information can indicate a width of Wsamples and a height of H samples of the CU.

At (S2720), the CU can be partitioned into SPUs, for example, when atleast one of the width W and the height H of the CU is larger than theprocessing data unit size K, such as described with reference to FIGS.24-26 . Based on the processing data unit size K and the size of the CU,a size of the SPUs can be determined. A width of the SPUs can be aminimum one of W and K, and a height of the SPUs can be a minimum one ofH and K. Accordingly, the CU can be partitioned into the SPUs eachhaving the determined width and height. For example, when W is 128, H is64, and K is 64, the CU can be divided into a first SPU of 64×64 and asecond SPU of 64×64. For example, the processing data unit can be aVPDU, and thus K can be a VPDU size.

At (S2730), one or more partitioning structures to partition each of theSPUs can be determined, for example, based on one or a combination ofthe width and the height of the SPUs and a maximum TU size of M samples.In an example, at least one of the width and the height of the SPUs islarger than M.

As described above, any suitable partitioning structure can be used topartition or split each of the SPUs. In an example, when the width andthe height of the SPU are larger than M, the one or more partitioningstructures is determined to be a quadtree partitioning structure. In anexample, when the width of the SPU is larger than M and the height ofthe SPU is not larger than M, the one or more partitioning structures isdetermined to be a vertical binary tree partitioning structure. In anexample, when the height of the SPU is larger than M and the width ofthe SPU is not larger than M, the one or more partitioning structures isdetermined to be a horizontal binary tree partitioning structure.

At (S2740), each of the SPUs can be partitioned into TUs based on thedetermined one or more partitioning structures. In an example, therespective SPU can be recursively partitioned into the TUs using thedetermined one or more partitioning structures.

At (S2750), the TUs of the SPUs are processed according to a processingorder. For example, the SPUs can be processed according to the firstorder, and the TUs in each of the SPUs can be processed according to thesecond order, as described above. Residual data of each TU can bedetermined by various decoding operations (e.g., entropy decoding oftransform coefficients, inverse quantization or de-quantization, inversetransforming, and/or the like). The process (2700) can proceed to(S2799) and terminate.

The process (2700) is described using a CU as an example. The process(2700) can be suitably adapted for a CB, such as a luma block, a chromablock, or the like. For purposes of brevity, the description for a CB isomitted.

The process (2700) can be suitably adapted. For example, one or moresteps can be modified, omitted, or combined. For example, steps (S2730)and (S2740) can be combined into a single step. Additional step(s) canalso be added. An order that the process (2700) is executed can also bemodified.

IV. Computer System

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 28 shows a computersystem (2800) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 28 for computer system (2800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (2800).

Computer system (2800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (2801), mouse (2802), trackpad (2803), touchscreen (2810), data-glove (not shown), joystick (2805), microphone(2806), scanner (2807), camera (2808).

Computer system (2800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (2810), data-glove (not shown), or joystick (2805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (2809), headphones(not depicted)), visual output devices (such as screens (2810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (2800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(2820) with CD/DVD or the like media (2821), thumb-drive (2822),removable hard drive or solid state drive (2823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (2800) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (2849) (such as, for example USB ports of thecomputer system (2800)); others are commonly integrated into the core ofthe computer system (2800) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (2800) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (2840) of thecomputer system (2800).

The core (2840) can include one or more Central Processing Units (CPU)(2841), Graphics Processing Units (GPU) (2842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(2843), hardware accelerators for certain tasks (2844), and so forth.These devices, along with Read-only memory (ROM) (2845), Random-accessmemory (2846), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (2847), may be connectedthrough a system bus (2848). In some computer systems, the system bus(2848) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (2848),or through a peripheral bus (2849). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (2841), GPUs (2842), FPGAs (2843), and accelerators (2844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(2845) or RAM (2846). Transitional data can be also be stored in RAM(2846), whereas permanent data can be stored for example, in theinternal mass storage (2847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (2841), GPU (2842), massstorage (2847), ROM (2845), RAM (2846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (2800), and specifically the core (2840) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (2840) that are of non-transitorynature, such as core-internal mass storage (2847) or ROM (2845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (2840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(2840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (2846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (2844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   ASIC: Application-Specific Integrated Circuit-   BMS: benchmark set-   CANBus: Controller Area Network Bus-   CBF: Coded Block Flag-   CD: Compact Disc-   CPUs: Central Processing Units-   CRT: Cathode Ray Tube-   CTBs: Coding Tree Blocks-   CTUs: Coding Tree Units-   CU: Coding Unit-   DVD: Digital Video Disc-   FPGA: Field Programmable Gate Areas-   GOPs: Groups of Pictures-   GPUs: Graphics Processing Units-   GSM: Global System for Mobile communications-   HEVC: High Efficiency Video Coding-   HRD: Hypothetical Reference Decoder-   ISP: Intra Sub-Partitions-   IC: Integrated Circuit-   JEM: joint exploration model-   LAN: Local Area Network-   LCD: Liquid-Crystal Display-   LTE: Long-Term Evolution-   MPM: Most Probable Mode-   MV: Motion Vector-   OLED: Organic Light-Emitting Diode-   PBs: Prediction Blocks-   PCI: Peripheral Component Interconnect-   PLD: Programmable Logic Device-   PUs: Prediction Units-   RAM: Random Access Memory-   ROM: Read-Only Memory-   SBT: Sub-block Transform-   SEI: Supplementary Enhancement Information-   SNR: Signal Noise Ratio-   SSD: solid-state drive-   TUs: Transform Units,-   USB: Universal Serial Bus-   VPDU: Virtual Pipeline Data Unit-   VUI: Video Usability Information-   VVC: versatile video coding

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding coded information of a coding block (CB) in apicture from a coded video bitstream, the coded information indicating awidth of the CB as W samples and a height of the CB as H samples;determining a maximum transform unit (TU) size M based on whether atleast one of the width W of the CB or the height H of the CB is greaterthan 64, the maximum TU size M being equal to 64 responsive to the atleast one of the width W of the CB or the height H of the CB beinggreater than 64, and equal to a maximum CB size responsive to the widthW of the CB and the height H of the CB not being greater than 64;determining a width parameter based on whether the width W of the CB isgreater than the maximum TU size M, the width parameter being equal tohalf of the width W of the CB responsive to the width W of the CB beinggreater than the maximum TU size M, and the width parameter being equalto the width W of the CB responsive to the width W of the CB not beinggreater than the maximum TU size M; determining a height parameter basedon whether the height H of the CB is greater than the maximum TU size M,the height parameter being equal to half of the height H of the CBresponsive to the height H of the CB being greater than the maximum TUsize M, and the height parameter being equal to the height H of the CBresponsive to the height H of the CB not being greater than the maximumTU size; determining which partitioning structure from among pluralpartitioning structures is selected to partition the CB based on thewidth W of the CB, the height H of the CB, and the maximum TU size M,the selected partitioning structure partitioning the CB based on thedetermined width and height parameters and the plural partitioningstructures comprising a vertical binary tree partitioning structure anda horizontal binary tree partitioning structure; and recursivelypartitioning the CB into a plurality of TUs until a size of each TU isless than or equal to M×M based on the partitioning structure that isdetermined as selected from among the plural partitioning structures. 2.The method of claim 1, wherein the plural partitioning structuresfurther comprises a quadtree partitioning structure; the selectedpartitioning structure is the vertical binary tree partitioningstructure in response to the width W being greater than M, the height Hnot being larger than M, and the width W being greater than the heightH; the selected partitioning structure is the horizontal binary treepartitioning structure in response to the height H being greater than M,the width W not being larger than M, and the height H being greater thanthe width W; and the selected partitioning structure is the quadtreepartitioning structure in response to both the width W and the height Hof the CB being larger than M.
 3. The method of claim 1, wherein themaximum TU size M is 32; the width W of the CB is 64 and the height H ofthe CB is equal to M; the selected partitioning structure is determinedas the vertical binary tree partitioning structure in the pluralpartitioning structures; and the recursively partitioning the CBincludes partitioning the CB into two TUs based on the vertical binarytree partitioning structure, each TU having a size of 32×32.
 4. Themethod of claim 1, wherein the maximum TU size M is 32; the height H ofthe CB is 64 and the width W of the CB is equal to M; the selectedpartitioning structure is determined as the horizontal binary treepartitioning structure in the plural partitioning structures; and therecursively partitioning the CB includes partitioning the CB into twoTUs based on the horizontal binary tree partitioning structure, each TUhaving a size of 32×32.
 5. The method of claim 1, further comprising:processing the TUs according to a scan order that is one of (i) a rasterscan order, (ii) a vertical scan order, (iii) a zig-zag order, and (iv)a diagonal scan order, wherein the scan order is based on a size of theCB.
 6. The method of claim 5, wherein the scan order is the raster scanorder, and the scan order of the TUs is the same as a scan order ofcoding blocks in the picture, the TUs being included in one of thecoding blocks in the picture.
 7. The method of claim 5, wherein W is128, H is 64, and M is 32; and the scan order is the raster scan order.8. The method of claim 1, wherein at least two TUs are configured to beprocessed simultaneously at different stages of a multi-stage pipeline.9. The method of claim 1, wherein the determining comprises: determiningwhich partitioning structure from among the plurality of partitioningstructures is selected to partition the CB based on the width W of theCB, the height H of the CB, the maximum transform unit (TU) size M, anda comparison of the height H and the width W.
 10. The method of claim 1,wherein the selected partitioning structure is the horizontal binarytree partitioning structure that partitions the CB into two partitionshaving sizes of W×H/2 in response to the height H being greater than themaximum TU size M and the height H being greater than the width W. 11.An apparatus for video decoding, comprising: processing circuitryconfigured to: decode coded information of a coding block (CB) in apicture from a coded video bitstream, the coded information indicating awidth of the CB as W samples and a height of the CB as H samples;determine a maximum transform unit (TU) size M based on whether at leastone of the width W of the CB or the height H of the CB is greater than64, the maximum TU size M being equal to 64 responsive to the at leastone of the width W of the CB or the height H of the CB being greaterthan 64, and equal to a maximum CB size responsive to the width W of theCB and the height H of the CB not being greater than 64; determine awidth parameter based on whether the width W of the CB is greater thanthe maximum TU size M, the width parameter being equal to half of thewidth W of the CB responsive to the width W of the CB being greater thanthe maximum TU size M, and the width parameter being equal to the widthW of the CB responsive to the width W of the CB not being greater thanthe maximum TU size M; determine a height parameter based on whether theheight H of the CB is greater than the maximum TU size M, the heightparameter being equal to half of the height H of the CB responsive tothe height H of the CB being greater than the maximum TU size M, and theheight parameter being equal to the height H of the CB responsive to theheight H of the CB not being greater than the maximum TU size; determinewhich partitioning structure from among plural partitioning structuresis selected to partition the CB based on the width W of the CB, theheight H of the CB, and the maximum TU size M, the selected partitioningstructure partitioning the CB based on the determined width and heightparameters and the plural partitioning structures comprising a verticalbinary tree partitioning structure and a horizontal binary treepartitioning structure; and recursively partition the CB into aplurality of TUs until a size of each TU is less than or equal to M×Mbased on the partitioning structure that is determined as selected fromamong the plural partitioning structures.
 12. The apparatus of claim 11,wherein the plural partitioning structures further comprises a quadtreepartitioning structure; both the width W and the height H of the CB arelarger than M; and the processing circuitry is further configured to:select the partitioning structure to be the quadtree partitioningstructure in the plural partitioning structures; and partition the CBinto the TUs based on the quadtree partitioning structure.
 13. Theapparatus of claim 11, wherein the maximum TU size M is 32; the width Wof the CB is 64 and the height H of the CB is equal to M; and theprocessing circuitry is further configured to: select the partitioningstructure to be the vertical binary tree partitioning structure in theplural partitioning structures; and partition the CB into two TUs basedon the vertical binary tree partitioning structure, each TU having asize of 32×32.
 14. The apparatus of claim 11, wherein the maximum TUsize M is 32; the height H of the CB is 64 and the width W of the CB isequal to M; and the processing circuitry is further configured to:select the partitioning structure to be the horizontal binary treepartitioning structure in the plural partitioning structures; andpartition the CB into two TUs based on the horizontal binary treepartitioning structure, each TU having a size of 32×32.
 15. Theapparatus of claim 11, wherein the processing circuitry is furtherconfigured to: process the TUs according to a scan order that is one of(i) a raster scan order, (ii) a vertical scan order, (iii) a zig-zagorder, and (iv) a diagonal scan order, wherein the scan order is basedon a size of the CB.
 16. The apparatus of claim 15, wherein the scanorder is the raster scan order, and the scan order of the TUs is thesame as a scan order of coding blocks in the picture, the TUs beingincluded in one of the coding blocks in the picture.
 17. The apparatusof claim 15, wherein W is 128, H is 64, and M is 32; and the scan orderis the raster scan order.
 18. The apparatus of claim 11, wherein theselected partitioning structure is the horizontal binary treepartitioning structure that partitions the CB into two partitions havingsizes of W×H/2 in response to the height H being greater than themaximum TU size M and the height H being greater than the width W. 19.The apparatus of claim 15, wherein a scan order of coding blocks in thepicture is another one of (i) the raster scan order, (ii) the verticalscan order, (iii) the zig-zag order, and (iv) the diagonal scan order,the TUs being included in one of the coding blocks in the picture.
 20. Anon-transitory computer-readable storage medium storing a programexecutable by at least one processor to: decode coded information of acoding block (CB) in a picture from a coded video bitstream, the codedinformation indicating a width of the CB as W samples and a height ofthe CB as H samples; determine a maximum transform unit (TU) size Mbased on whether at least one of the width W of the CB or the height Hof the CB is greater than 64, the maximum TU size M being equal to 64responsive to the at least one of the width W of the CB or the height Hof the CB being greater than 64, and equal to a maximum CB sizeresponsive to the width W of the CB and the height H of the CB not beinggreater than 64; determine a width parameter based on whether the widthW of the CB is greater than the maximum TU size M, the width parameterbeing equal to half of the width W of the CB responsive to the width Wof the CB being greater than the maximum TU size M, and the widthparameter being equal to the width W of the CB responsive to the width Wof the CB not being greater than the maximum TU size M; determine aheight parameter based on whether the height H of the CB is greater thanthe maximum TU size M, the height parameter being equal to half of theheight H of the CB responsive to the height H of the CB being greaterthan the maximum TU size M, and the height parameter being equal to theheight H of the CB responsive to the height H of the CB not beinggreater than the maximum TU size; determine which partitioning structurefrom among plural partitioning structures is selected to partition theCB based on the width W of the CB, the height H of the CB, and themaximum size M, the selected partitioning structure partitioning the CBbased on the determined width and height parameters and the pluralpartitioning structures comprising a vertical binary tree partitioningstructure and a horizontal binary tree partitioning structure; andrecursively partition the CB into a plurality of TUs until a size ofeach TU is less than or equal to M×M based on the partitioning structurethat is determined as selected from among the plural partitioningstructures.